Planar light source, display device, portable terminal device, and ray direction switching element

ABSTRACT

A planar light source includes a large variable width of an irradiation angle of illumination light, a display device having a large variable width of an angle of field that uses the planar light source, a portable terminal device that uses the display device, and a ray direction switching element that is incorporated in the planar light source. A beam direction regulating element (a louver), which controls a direction of light, and a transparent and scattering switching element, which can switch the transparent state and the scattering state according to ON and OFF of an applied voltage, are provided between a backlight and a liquid crystal panel, whereby it is possible to increase a variable width of an irradiation angle of light in the planar light source and increase a variable width of an angle of field of the liquid crystal display device that uses the planar light source.

RELATED APPLICATIONS

The present Application is a Divisional Application of U.S. patentapplication Ser. No. 11/134,299 which was filed on May 23, 2005 now U.S.Pat. No. 7,349,043 and is incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

[Technical Field]

The present invention relates to a planar light source, a displaydevice, a portable terminal device, and a ray direction switchingelement, and in particular, to a planar light source that can change anirradiation angle of illumination light, a display device that canchange an angle of field using the planar light source, a portableterminal device that uses the display device, and a ray directionswitching element that is incorporated in the planar light source.

2. Description of the Related Art

[Background Art]

In accordance with the development of technologies in recent years, aliquid crystal display device (LCD), which is wide in an angle of field,that is, visually recognizable in a wide angle range, has been put topractical use. In addition, a portable information terminal mounted withthe LCD is also widely used. In such a portable information terminal, itis desirable that the angle of field of the LCD is wide when a userlooks at information displayed on the LCD with other people. On theother hand, in the portable information terminal, the user often doesnot want other people to peep at displayed information. In such a case,it is desirable that the angle of field of the LCD is narrow. In thisway, the angle of field is required to be wide and narrow depending on astate of use of the LCD. Conventionally, LCDs meeting such a demand havebeen proposed.

FIGS. 24( a) and 24(b) schematically show a first conventional liquidcrystal display device that is described in Japanese Patent Laid-OpenNo. 6-59287. FIG. 24( a) shows the liquid crystal display device at thetime when a voltage is not applied thereto. FIG. 24( b) shows the liquidcrystal display device at the time when a voltage is applied thereto. Asshown in FIGS. 24( a) and 24(b), the first conventional liquid crystaldisplay device includes a liquid crystal panel in which a liquid crystalmaterial (not shown) is sealed by transparent substrates 102 and 108. Apolarizing plate 101 is provided on one surface of this liquid crystalpanel. On the other surface, a guest host liquid crystal cell 131, inwhich a liquid crystal material consisting of liquid crystal molecules131 a and elongate pigment molecules 131 b are sealed by two transparentsubstrates 114 provided with transparent electrodes 110 on surfacesthereof, is provided. The pigment molecules 131 b have a larger amountof absorption of light in a minor axis direction of the molecules thanin a major axis direction thereof. When a voltage is not applied to theguest host liquid crystal cell 131, the liquid crystal molecules 131 aand the elongate pigment molecules 131 b are arranged to be parallel tothe surfaces of the transparent substrates 114 in a longitudinaldirection. When a voltage is applied to the guest host liquid crystalcell 131, the liquid crystal molecules 131 a and the elongate pigmentmolecules 131 b are arranged to be perpendicular to the surfaces of thetransparent substrates 114 in the longitudinal direction. The polarizingplate 101 is provided on a surface on the opposite side of a surfaceopposed to the liquid crystal panel of the guest host liquid crystalcell 131.

In the first conventional liquid crystal display device constituted inthis way, which is described in Japanese Patent Laid-Open No. 6-59287,light in a wide angle range passes through the liquid crystal panel tobe made incident on the guest host liquid crystal cell 131. When animage is displayed at a wide angle of field, a voltage is not applied tothe guest host liquid crystal cell 131 to make a light absorbingdirection of the guest host liquid crystal cell 131 coincident with anabsorbing direction of the polarizing plate 101, whereby the lightpasses through the guest host liquid crystal cell 131 directly.Consequently, it is possible to visually recognize a display screen in awide angle range.

When an image is displayed at a narrow angle of field, when a voltage isapplied to the guest host liquid crystal cell 131, the pigment molecules131 b are arranged to be perpendicular to the surfaces of thetransparent substrates 114 in the longitudinal direction, and an angleof incidence of light deviates largely from a direction perpendicular tothe surfaces of the transparent substrates 114. This light is absorbedby the pigment molecules 131 b and does not pass through the guest hostliquid crystal cell 131. Therefore, even if an angle distribution oflight made incident on the display device is wide, an angle distributionof emitted light is narrowed by absorption of the guest host liquidcrystal. Consequently, it is possible to reduce a size of a visuallyrecognizable display screen.

FIG. 25 is a diagram schematically showing a second conventional liquidcrystal display device that is described in Japanese Patent Laid-OpenNo. 10-197844. The second conventional liquid crystal display deviceincludes a backlight 113, as shown in FIG. 25. A PDLC cell 136, in whicha Polymer Dispersed Liquid Crystal (PDLC) layer 111 is sandwiched by twotransparent substrates 109, is provided on the backlight 113. Apolarizing plate 101 is provided on the PDLC cell 136, and a TwistedNematic-Liquid Crystal Display (TN-LCD) is provided on the polarizingplate 101. A guest host liquid crystal cell is provided on the TN-LCD,and the polarizing plate 101 is provided on the guest host liquidcrystal cell. This guest host liquid crystal cell has the same structureas the guest host liquid crystal cell that is used in the firstconventional liquid crystal display device described in Japanese PatentLaid-Open No. 6-59287.

In the second conventional liquid crystal display device constituted inthis way, which is described in Japanese Patent Laid-Open No. 10-197844,wide field of view display and narrow field of view display are switchedby switching ON and OFF of a voltage applied to the guest host liquidcrystal cell. In addition, transmission and reflection of light isswitched by switching ON and OFF of a voltage applied to the PDLC cellto adjust brightness of a display screen.

Japanese Patent Laid-Open No. 11-142819 discloses a liquid crystaldisplay device in which a condensing element consisting of a prism sheetand a light scattering element consisting of a PDLC cell are providedbetween a light source and a liquid crystal panel. Japanese PatentLaid-Open No. 11-142819 mentions that it is possible to switch a narrowangle of field and a wide angle of field by increasing directivity oflight with the prism sheet and, then, transmitting or scattering lightfrom the prism sheet with the PDLC cell. In addition, Japanese PatentLaid-Open No. 9-105907 discloses a similar liquid crystal display devicein which an optical element consisting of a PDLC cell is providedbetween a light source and a liquid crystal panel.

On the other hand, conventionally, a high directivity backlight, inwhich an irradiation range of illumination light is fixed butdirectivity in a specific direction such as the front direction isimproved, has been developed (see, for example, monthly magazine“Display” May 2004, pages 14 to 17). FIG. 26 is a perspective viewshowing a conventional high directivity backlight 213 described in themonthly magazine “Display” May 2004, pages 14 to 17. As shown in FIG.26, in this conventional high directivity backlight 213, an LED 201 isarranged in one location where a light guide plate 202 is provided, anda linear micro-prism is arranged concentrically around the LED 201 inthe light guide plate 202. A prism sheet 203, in which a prism structureis also arranged concentrically around the LED 201, is arranged on alight emission surface of the light guide plate 202. In addition, areflection sheet 204 is arranged on a surface on the opposite side ofthe surface of the light guide plate 202 on which the prism sheet 203 isprovided.

Exit light from the LED 201 is made incident on the light guide plate202 and emitted radially along the surface of the light guide plate 202by the linear micro-prism formed in the light guide plate 202. At thispoint, the LED 201 is arranged in one location of the light guide plate202, and a longitudinal direction of the linear micro-prism formed inthe light guide plate 202 is arranged to be substantially perpendicularto the LED 201. Thus, even if light guided through the light guide plate202 hits the linear micro-prism, the light is not deflected in thelongitudinal direction of the linear micro-prism but travels linearlyand radially around the LED 201. The light emitted from the light guideplate 202 is refracted by the prism sheet 203 and deflected in avertical direction with respect to the light emission surface of thelight guide plate 202. Consequently, a high directivity backlight, inwhich directivity is improved two-dimensionally in a front direction, isrealized.

DISCLOSURE OF THE INVENTION Problems to Solved by the Invention

However, the conventional techniques described above has problemsdescribed below. In the liquid crystal display device described inJapanese Patent Laid-Open No. 6-59287, a difference of an amount ofabsorption of light is small in the minor axis direction and the majoraxis direction of the pigment molecules in the guest host liquid crystalcell. In other words, a pigment dichroic ratio is low. In addition,liquid crystal molecules near the transparent substrates do not stand atthe time of voltage application, and the pigment molecules arranged inparallel to the transparent substrates remains. Consequently, in theguest host liquid crystal cell at the time of voltage application,efficiency of absorbing light, an incident angle of which deviateslargely from the direction perpendicular to the surfaces of thetransparent substrates, falls, and an angle of field at the time of thenarrow field of view display increases.

In addition, in the liquid crystal display device described in JapanesePatent Laid-Open No. 10-197844, the wide field of view display and thenarrow field of view display are also switched by switching ON and OFFof a voltage applied to the guest host liquid crystal. Consequently, thesame problems as the liquid crystal display device described in JapanesePatent Laid-Open No. 6-59287 occur.

Moreover, in the liquid crystal display device described in JapanesePatent Laid-Open No. 11-142819, light from a light source is condensedby the prism sheet, that is, directivity of light is improved. The lightwith high directivity passes through the PDLC cell directly, whereby asize of a visually recognizable display screen is reduced. However,since the prism sheet does not have a sufficient effect for improvingdirectivity of light, an angle of field at the time of the narrow fieldof view display increases. In other words, other people peep atdisplayed information.

SUMMARY OF THE INVENTION

The invention has been devised in view of such problems, and it is anobject of the invention to provide a planar light source having a largevariable width of an irradiation angle of illumination light, a displaydevice having a large variable width of an angle of field that uses theplanar light source, a portable terminal device that uses the displaydevice, and a ray direction switching element that is incorporated inthe planar light source.

Means for Solving the Problems

A planar light source in accordance with the invention includes: abacklight that emits light in a planar shape; a ray direction regulatingelement that regulates a direction of light made incident from thebacklight and emits the light and in which a transparent area fortransmitting light and an absorption area for absorbing light are formedalternately in a direction perpendicular to a light regulating directionthereof; and a transparent and scattering switching element that iscapable of switching a state in which light made incident from the raydirection regulating element is transmitted and a state in which thelight is scattered.

In the invention, the beam direction regulating element, which controlsa direction of light, and the transparent and scattering switchingelement, which can switch the transparent and the scattering stateaccording to ON and OFF of an applied voltage, are provided between thebacklight and a liquid crystal panel, whereby it is possible to increasea variable width of an irradiation angle of light in the planar lightsource.

It is preferable that an emitting direction of light emitted by thebacklight spreads radially in an elliptical shape with respect to adirection perpendicular to an emission surface, and the transparent areaand the absorption area of the ray direction regulating element areformed alternately in a direction parallel to a long diameter directionof the ellipse.

It is preferable that an emitting direction of light emitted from theback light spreads radially in an elliptical shape with respect to adirection perpendicular to an emission surface and, in the ray directionregulating element, the transparent area and the absorption area areformed alternately in a direction parallel to a short diameter directionof the ellipse. Consequently, since an amount of light of the backlightpassing through the ray direction regulating element increases, it ispossible to realize a bright planar light source.

An emitting direction of light emitted by the backlight may be condensedradially in a circular shape with respect to a direction perpendicularto an emission surface. Consequently, since a loss of absorption oflight by the ray direction regulating element can be reduced, it ispossible to realize bright display. In addition, since directivity ofthe backlight is two-dimensional, it is also possible to switch thenarrow field of view display and the wide field of view displayconcerning a direction orthogonal to the direction in which thetransparent area and the absorption area of the ray direction regulatingelement are arranged alternately.

It is preferable that, in the transparent and scattering switchingelement, a polymer dispersed liquid crystal layer, in which liquidcrystal molecules are dispersed in a polymer film, is sandwiched betweena pair of flat electrodes, and the polymer dispersed liquid crystallayer is in a state in which the polymer dispersed liquid crystal layertransmits incident light when a voltage is applied between the flatelectrodes and in a state in which the polymer dispersed liquid crystallayer scatters incident light when a voltage is not applied between theflat electrodes. Consequently, since the transparent and scatteringswitching element does not consume electric power in the state in whichthe transparent and scattering switching element scatters incidentlight, the electric power is allocated to a backlight light source.Thus, it is possible to improve brightness of the planar light source atthe time of the scattering state.

An orientation state of the liquid crystal molecules at the time when avoltage is applied thereto may be held after the application of thevoltage is stopped.

The transparent and scattering switching element and the ray directionregulating element may be formed integrally. Consequently, since the raydirection regulating element can be supported by the transparent andscattering switching element, it is possible to realize a highly stableand thin planar light source.

The transparent and scattering switching element and the ray directionregulating element may have a common substrate.

A substrate of the ray direction regulating element may be only asubstrate common to the ray direction regulating element and thetransparent and scattering switching element. Consequently, it ispossible to further reduce thickness of the planar light source. Inaddition, it is preferable that an amount of light of the backlight andthe transparent and scattering states of the transparent and scatteringswitching element can be set independently. Consequently, it is possibleto set intensity and directivity of light emitted from the planar lightsource in various ways.

It is also possible that the transparent and scattering switchingelement is in the state in which the transparent and scatteringswitching element scatters incident light when a voltage is not appliedbetween the flat electrodes, and in which a voltage is applied to thetransparent and scattering switching element when the transparent andscattering switching element is used in the scattering state.Consequently, it is possible to increase a front luminance withoutsignificantly decreasing a luminance in an oblique direction at the timewhen the transparent and scattering switching element is used in thescattering state.

A display device in accordance with the invention includes: a backlightthat emits light in a planar shape; a ray direction regulating elementthat regulates a direction of light made incident from the backlight andemits the light and in which a transparent area for transmitting lightand an absorption area for absorbing light are formed alternately in adirection perpendicular to a light regulating direction thereof; atransparent and scattering switching element that is capable ofswitching a state in which light made incident from the ray directionregulating element is transmitted and a state in which the light isscattered; and a liquid crystal panel that displays an image using lightmade incident from the transparent and scattering switching element.

In the invention, the beam direction regulating element, which controlsa direction of light, and the transparent and scattering switchingelement, which can switch the transparent and the scattering stateaccording to ON and OFF of an applied voltage, are provided between thebacklight and a liquid crystal panel, whereby it is possible to increasea variable width of an angle of field of the display device.

It is preferable that an emitting direction of light emitted by thebacklight spreads radially in an elliptical shape with respect to adirection perpendicular to an emission surface and, in the ray directionregulating element, the transparent area and the absorption area areformed alternately in a direction parallel to a long diameter directionof the ellipse.

The white light source may be constituted by a blue LED and a yellowphosphor to adjust an amount of light with pulse modulation.Consequently, it is possible to control chromaticity change of thedisplay device when an amount of light of the white light source isadjusted simultaneously with switching of transparent and scattering.

A direction in which the transparent area and the absorption area of theray direction regulating element are formed alternately and a pixelarrangement direction of the display panel do not have to be parallel toeach other. Consequently, it is possible to reduce moiré due to the raydirection regulating element and the display panel.

The display panel may be a liquid crystal panel, and the liquid crystaldisplay panel may be a panel of a lateral electric field mode, amulti-domain vertical orientation mode, or a film compensation TN mode.Consequently, it is possible to control tone reversal and improvevisibility at the time when the transparent and scattering switchingelement is in the scattering state.

The portable terminal device may have adjusting means that can change anamount of the backlight and the transparent and scattering states of thetransparent and scattering switching element independently from eachother. Consequently, a user can set an optimum state according to anenvironment of use of the portable terminal device.

The portable terminal device may have electric power accumulating means,residual amount detecting means for electric power accumulated in theelectric power accumulating means, and control means that automaticallychanges an amount of the backlight and the transparent and scatteringstates of the transparent and scattering switching element on the basisof detected residual amount information. When the transparent andscattering element is brought into the transparent state, since anamount of light of the backlight can be reduced, it is possible toreduce power consumption when residual battery power is low and extendan operating time of the portable terminal device.

The transparent area and the absorption area of the ray directionregulating element may be formed alternately in a lateral direction ofthe portable terminal device. Consequently, it is possible to increase avariable width of an angle of field in the lateral direction of theportable terminal device.

A ray direction switching element in accordance with the invention ischaracterized in that a ray direction regulating element, whichregulates a direction of incident light and emits light, and atransparent and scattering switching element, which is capable ofswitching a state in which light made incident from the ray directionregulating element is transmitted and a state in which the light isscattered, are integrally formed. Consequently, since the ray directionregulating element can be supported by the transparent and scatteringswitching element, it is possible to realize a highly stable and thinray direction switching element.

In the ray direction switching element, the transparent and scatteringswitching element and the ray direction regulating element may be formedon a common substrate. A substrate of the ray direction regulatingelement may be only a substrate common to the ray direction regulatingelement and the transparent and scattering switching element.

Advantage of the Invention

According to the invention, the ray direction regulating element, thatcontrols a direction of light, and the transparent and scatteringswitching element, which can switch the transparent and scatteringstates by turning ON and OFF an applied voltage, are provided betweenthe backlight and the liquid crystal panel, whereby it is possible toincrease a variable width of an irradiation angle of light in the planarlight source and increase a variable width of an angle of field of theliquid crystal display device that uses the planar light source.

BRIEF DESCRIPTION OF THE DRAWINGS Brief Description of the Drawings

FIG. 1 is a sectional view showing a liquid crystal display device inaccordance with a first embodiment of the invention;

FIG. 2 is a perspective view showing an example of a backlight that isused in the liquid crystal display device in accordance with the firstembodiment of the invention;

FIG. 3 is a diagram showing a direction of light emitted from thebacklight;

FIG. 4 is a plan view showing an example of a louver that is used in theliquid crystal display device in accordance with the first embodiment ofthe invention;

FIG. 5 is a diagram showing a light distribution characteristic at thetime of a wide angle of field of the liquid crystal display device inaccordance with the first embodiment of the invention;

FIG. 6 is a diagram showing a light distribution characteristic at thetime of a narrow angle of field of the liquid crystal display device inaccordance with the first embodiment;

FIG. 7 is a plan view showing an example of a louver that is used in aliquid crystal display device in accordance with a first modification ofthe first embodiment of the invention;

FIG. 8 is a plan view showing an example of a louver that is used in aliquid crystal display device in accordance with a second modificationof the first embodiment of the invention;

FIG. 9 is a diagram showing a light distribution characteristic at thetime of a wide angle of field of a liquid crystal display device inaccordance with a third modification of the first embodiment of theinvention;

FIG. 10 is a diagram showing a light distribution characteristic at thetime of a narrow angle of field of the liquid crystal display device inaccordance with the third modification of the first embodiment of theinvention;

FIG. 11 is a sectional view showing a liquid crystal display device inaccordance with a second embodiment of the invention;

FIG. 12 is a sectional view showing a liquid crystal display device inaccordance with a third embodiment of the invention;

FIG. 13 is a sectional view showing a liquid crystal display device inaccordance with a fourth embodiment of the invention;

FIG. 14 is a sectional view showing a liquid crystal display device inaccordance with a fifth embodiment of the invention;

FIG. 15 is a sectional view showing a liquid crystal display device inaccordance with a sixth embodiment of the invention;

FIG. 16 is a sectional view showing a liquid crystal display device inaccordance with a seventh embodiment of the invention;

FIG. 17 is a sectional view showing a liquid crystal display device inaccordance with an eighth embodiment of the invention;

FIG. 18 is a sectional view showing a liquid crystal display device inaccordance with a ninth embodiment of the invention;

FIG. 19 is a sectional view showing a liquid crystal display device inaccordance with a tenth embodiment of the invention;

FIG. 20 is a graph showing a result of an experiment in which a slightvoltage is applied to a transparent and scattering switching element ina scattering state to adjust a scattering property;

FIG. 21 is a perspective view showing a portable terminal device mountedwith a liquid crystal display device of the invention;

FIG. 22 is a plan view showing a transparent and scattering switchingelement of a liquid crystal display device in accordance with a twelfthembodiment of the invention;

FIG. 23 is a plan view showing a liquid crystal display device in whicha direction in which a transparent area and an absorption area of a raydirection regulating element are formed alternately and a pixelarrangement direction of a liquid crystal display panel are not parallelto each other;

FIG. 24( a) is a diagram schematically showing a first conventionalliquid crystal display device at the time when a voltage is not appliedthereto;

FIG. 24( b) is a diagram schematically showing a first conventionalliquid crystal display device at the time when a voltage is appliedthereto;

FIG. 25 is a diagram schematically showing a second conventional liquidcrystal display device; and

FIG. 26 is a perspective view showing a conventional high directivitybacklight.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Best Mode for CarryingOut the Invention

Embodiments of the invention will be hereinafter explained specificallywith reference to the accompanying drawings. First, a first embodimentof the invention will be explained. FIG. 1 is a sectional view showing aliquid crystal display device in accordance with the first embodiment.FIG. 2 is a perspective view showing an example of a backlight that isused in the liquid crystal display device in accordance with the firstembodiment. FIG. 3 is a diagram showing a direction of light emittedfrom the backlight. FIG. 4 is a plan view showing an example of a louverthat is used as a ray direction regulating element in the liquid crystaldisplay device in accordance with the first embodiment. FIG. 5 is adiagram showing a light distribution characteristic at the time of awide angle of field of the liquid crystal display device in accordancewith the first embodiment. FIG. 6 is a diagram showing a lightdistribution characteristic at the time of a narrow angle of field ofthe liquid crystal display device.

As shown in FIG. 1, in the liquid crystal display device in accordancewith the first embodiment, a backlight 13 is provided, and a louver 12(a ray direction regulating element) is provided above the backlight 13.A transparent and scattering switching element 22 is provided above thelouver 12, and a liquid crystal panel 21 is provided above thetransparent and scattering switching element 22.

As shown in FIG. 2, a linear light source 36 of a prism shape isprovided along one end face of the backlight 13, and white LEDs 25 areprovided to be opposed to both ends thereof, respectively. The linearlight source 36 includes plural prisms (not shown), which are arrangedcyclically, to refract light, which is made incident on the linear lightsource 36 from the white LEDs 25, substantially orthogonally in adirection of the backlight 13 with the plural prisms. In this way, thelinear light source 36 emits linear light in the direction of thebacklight 13 from a side of the backlight 13. In addition, the backlight13 includes plural prisms (not shown) that are arranged cyclically in adirection orthogonal to a surface extending in parallel to the linearlight source 36 and opposed to the linear light source 36. These prismsrefract linear light made incident from the linear light source 36 in adirection orthogonal to one surface 37 of the backlight 13 and emitplanar light from the entire surface 37. Such a backlight 13 emitslight, of which light in a direction parallel to the linear light source36 has a wider angle than light in a direction orthogonal to the linearlight source 36.

As shown in FIG. 3, a direction 35 of light emitted from the backlight13 is defined by a polar angle θ and an azimuth φ. The polar angle θ isan angle formed by the direction 35 and a direction 34 perpendicular toa surface of the backlight 13. On a projection surface 13 parallel tothe backlight 13, when an X-Y rectangular coordinate with a point, wherethe direction 34 and the projection surface 33 cross each other, as anorigin O is assumed, the azimuth φ is an angle formed by a line, whichconnects an intersection where the direction 35 and the projectionsurface 33 cross each other and the origin O, and the X axis. In thisway, light emitted from the backlight 13 is diffused light, and θ and φhave wide distributions.

As shown in FIG. 1, the louver 12 is a ray direction regulating elementthat improves directivity of light emitted from the backlight 13. Thelouver 12 regulates a ray direction of broadening light made incidentfrom the backlight 13 in one direction and emits the light. This lightregulating direction is, for example, a direction perpendicular to asurface of the louver 12. Of the light emitted from the louver 12,directivity of light in a direction perpendicular to the surface of thelouver 12 (light regulating direction) is improved. In this case, thelight emitted with the direction thereof regulated by the louver 12broadens a little, although a polar angle θ is smaller than that of thelight emitted from the backlight 13 shown in FIG. 3.

In the louver 12, for example, a transparent area 12 a, which transmitslight, and an absorption area 12 b, which absorbs light, are formed tobe arranged alternately in a direction parallel to the surface of thelouver 12. The direction in which the transparent area 12 a and theabsorption area 12 b are arranged alternately is identical with, forexample, a direction in which the backlight 13 emits wide angle light,that is, a direction parallel to the linear light source 36. As shown inFIG. 4, viewed from a direction perpendicular to the surface of thelouver 12, the transparent area 12 a and the absorption area 12 b of astripe shape are arranged alternately. The louver 12 can adjust, forexample, thickness and an arrangement pitch of the transparent area 12 aand the absorption area 12 b and an absorption amount of light in theabsorption area 12 b to adjust an emission angle at the time whenincident light is emitted.

As shown in FIG. 1, in the transparent and scattering switching element22, a PDLC layer 11 formed by scattering liquid crystal molecules 11 bin a polymer matrix 11 a is put in electrodes 10, and a transparentsubstrate 9 is provided on the each electrode 10. A voltage is appliedto the PDLC layer 11, which is sandwiched between the electrodes 10, bythe electrodes 10, whereby an orientation state of liquid crystalmolecules in the PDLC layer 11 changes. The PDLC layer 11 is formed by,for example, exposing a mixture of a photo-curing resin and a liquidcrystal material to light and hardening the mixture. The transparent andscattering switching element 22 scatters or transmits light madeincident from the louver 12 and emits the light to the liquid crystalpanel 21.

In the liquid crystal panel 21, a polarizing panel 1, which polarizeslight made incident from the transparent and scattering switchingelement 22, is provided, and a transparent substrate 8 is provided onthe polarizing plate 1. A pixel electrode 7 defining a pixel area isprovided on the transparent substrate 8 in a matrix shape. A liquidcrystal layer 6 is provided to cover surfaces of the pixel electrode 7and the transparent substrate 8. A common electrode 5 for applying avoltage to the liquid crystal layer 6 is provided on the liquid crystallayer 6, and the transparent dielectric layer 4 is provided on thecommon electrode 5. In the transparent dielectric layer 4, a groove isformed in a position corresponding to an area of the surface of thetransparent substrate 8, which is not covered by the pixel electrode 7,and a black matrix 3, which prevents external light from being projectedon the liquid crystal panel, is provided in the groove. A transparentsubstrate 2 is provided to cover the transparent dielectric layer 4 andthe black matrix 3, and a polarizing plate 1, which polarizes emittedlight from the liquid crystal panel, is provided on the transparentsubstrate 2.

As shown in FIG. 5, light emitted from the backlight 13 has anelliptical distribution 38 spreading widely in an X direction comparedwith a Y direction. This emitted light distribution indicates that lightspreads largely as an area of a distribution area is larger. When lightof this distribution 38 is made incident on the louver 12, lightspreading in the X direction is absorbed by the louver 12 to change tolight of a distribution 39 with high directivity that is distributedsubstantially in a round shape. In the case of the wide field of viewdisplay, when the light of this distribution 39 is made incident on thetransparent and scattering switching element 22 in the scattering state,light of a circular distribution is uniformly scattered to change tolight of a circular distribution 40 that spreads more largely. The lightof this distribution 40 is transmitted through the liquid crystal panel21 and emitted to realize the wide field of view display.

As shown in FIG. 6, when light of the distribution 38 emitted from thebacklight 13 is made incident on the louver 12, light spreading in the Xdirection is absorbed by the louver 12 to change to light of thedistribution 39 with high directivity that is distributed insubstantially in a round shape. In the case of the narrow field of viewdisplay, when the light of this distribution 39 is made incident on thetransparent and scattering switching element 22 in the transparentstate, light of a circular distribution is transmitted through thetransparent and scattering switching element 22 directly and light ofthe distribution 39 is emitted. The light of this distribution 39 istransmitted through the liquid crystal panel 21 and emitted to realizethe narrow field of view display.

Next, an operation of the liquid crystal display device in accordancewith the first embodiment formed as described above will be explained.First, a case of the wide field of view display will be explained. Asshown in FIG. 1, light emitted from the backlight 13 is made incident onthe louver 12. As shown in FIG. 3, light emitted from the backlight 13is diffused light, and θ and φ have wide distributions. In the backlight13 shown in FIG. 2, as shown in FIG. 5, light emitted from the backlight13 has a larger value of θ in the case in which φ is close to 0 degreeor 180 degrees than in the case in which φ is close to 90 degrees or 270degrees. In other words, the light has the elliptical distribution 38spreading widely in the X direction compared with the Y direction. Whenthe light of this distribution 38 is made incident on the louver 12,light with large θ is absorbed by the absorption area 12 b of the louver12. Light with small θ is transmitted through the transparent area 11 a.Therefore, in light emitted from the louver 12, the light with large θis removed and light of the distribution 39 with a small distributionarea and high directivity is emitted.

As shown in FIG. 1, the light of the distribution 39 with highdirectivity emitted from the louver 12 is made incident on thetransparent and scattering switching element 22. In the case of the widefield of view display, a voltage is not applied to the PDLC layer 11.Consequently, the PDLC layer 11 is in a state in which the liquidcrystal molecules 11 b are scattered at random in the polymer matrix 11a, and the incident light is scattered. Therefore, as shown in FIG. 5,light of the circular distribution 39 is uniformly scattered by the PDLClayer 11 to change to light of the circular distribution 40 spreadingmore largely. In other words, the light, directivity of which isimproved by the louver 12, is scattered by the transparent andscattering switching element 22 to have lower directivity and change tolight with a wide angle. As shown in FIG. 1, the light of thedistribution 40 spreading in a wide range is made incident on the liquidcrystal panel 21 and emitted while keeping the distribution 40. In thisway, an image is displayed in a wide angle of field.

Next, a case of the narrow field of view display will be explained. Asshown in FIG. 6, as in the case of the wide field of view display, lighthaving the elliptical distribution 38 emitted from the backlight 13 ischanged to light of the distribution 39 with a small distribution areaand high directivity by the louver 12.

As shown in FIG. 1, the light of the distribution 39 is made incident onthe transparent and scattering switching element 22. In the case of thenarrow field of view display, a predetermined voltage is applied to thePDLC layer 11. Consequently, the PDLC layer 11 comes into thetransparent state in which the liquid crystal molecules 11 b scatteredin the polymer matrix 11 a are oriented. In other words, the PDLC layer11 transmits incident light directly. Therefore, as shown in FIG. 6, thelight of the circular distribution 39 is transmitted through the PDLClayer 11 directly. In other words, the light, directivity of which isimproved by the louver 12, is emitted from the transparent andscattering switching element 22 in a state of the distribution 39keeping high directivity. As shown in FIG. 1, the light of thedistribution 39 with high directivity is made incident on the liquidcrystal panel 21 and emitted while keeping the distribution 39. In thisway, an image is displayed at a narrow angle of field.

In this way, light with low directivity emitted from the backlight 13 isconverted into light with high directivity by the louver 12, and thelight with high directivity is transmitted or scattered by thetransparent and scattering switching element, which uses the PDLC layer,to switch the narrow field of view display and the wide field of viewdisplay. Consequently, it is possible to increase a variable width of anirradiation angle of light in the planar light source and increase avariable width of an angle of field of the liquid crystal display devicethat uses the planar light source.

Here, the same liquid crystal display device as the first embodiment isconstituted using the conventional prism sheet instead of the louver 12to measure a relation between an angle of field and a luminance in thecase of the narrow field of view display. A range of an angle of fieldof 0 degree, that is, an angle of field, at which a luminance of a valueequal to or larger than half a luminance at the time when the liquidcrystal display device is viewed from the front is obtained, is 30degrees to the left and the right. On the other hand, in the firstembodiment, a range of an angle of field, at which a luminance of avalue equal to or larger than half a luminance at the angle of field 0degree is obtained, is 20 degrees to the left and the right. In thisway, in the first embodiment, it is possible to realize the narrow fieldof view display effectively compared with the conventional technique.

Next, a first modification of the first embodiment of the invention willbe explained. FIG. 7 is a plan view showing an example of a louver thatis used in a liquid crystal display device in accordance with the firstmodification of the first embodiment. In the first embodiment describedabove, as shown in FIG. 4, the transparent area 12 a and the absorptionarea 12 b of a stripe shape are arranged alternately on the surface ofthe louver 12 when the louver 12 is viewed from a directionperpendicular to the surface. Thus, directivity of light made incidenton the louver 12 can be improved only in one direction. On the otherhand, in the first modification of the first embodiment, as shown inFIG. 7, a circular transparent area 12 a is arranged in the absorptionarea 12 b in a matrix shape when the louver 12 is viewed from adirection perpendicular to the surface of the louver 12. Consequently,it is possible to improve directivity of light made incident on thelouver 12 in various directions. Components, operations, and effects inthe first modification of the first embodiment other than thosedescribed above are the same as those in the first embodiment.

Next, a second modification of the first embodiment will be explained.FIG. 8 is a plan view showing an example of a louver that is used in aliquid crystal display device in accordance with the second modificationof the first embodiment. In the first modification of the firstembodiment, as shown in FIG. 7, the circular transparent area 12 a isarranged in the absorption area 12 b in a matrix shape. On the otherhand, in the second modification of the first embodiment, as shown inFIG. 8, a quadrangle transparent area 12 a is arranged in the absorptionarea 12 b in a matrix shape when the louver 12 is viewed from adirection perpendicular to the surface of the louver 12. The transparentarea 12 a is, for example, a square or a rectangle. Components,operations, and effects in the second modification of the firstembodiment other than those described above are the same as those in thefirst modification of the first embodiment.

Next, a third modification of the first embodiment of the invention willbe explained. FIG. 9 is a diagram showing a light distributioncharacteristic at the time of a wide angle of field of a liquid crystaldisplay device in accordance with a third modification of the firstembodiment. FIG. 10 is a diagram showing a light distributioncharacteristic at the time of a narrow angle of field.

In the first embodiment, as shown in FIG. 5, light emitted from thebacklight 13 has the elliptical distribution 38 spreading in the Xdirection widely compared with the Y direction. When the light of thisdistribution 38 is made incident on the louver 12, the light spreadingin the X direction is absorbed by the louver 12 to change to light ofthe distribution 39 with high directivity that is distributedsubstantially in a round shape. In the case of the wide field of viewdisplay, when the light of this distribution 39 is made incident on thetransparent and scattering switching element 22 in the scattering state,light of a circular distribution is uniformly scattered to change tolight of the circular distribution 40 spreading more largely. The lightof this distribution 40 is transmitted through the liquid crystal panel21 and emitted to realize the wide field of view display. In addition,as shown in FIG. 6, when light of the distribution 38 emitted from thebacklight 13 is made incident on the louver 12, light spreading in the Xdirection is absorbed by the louver 12 to change to light of thedistribution 39 with high directivity that is distributed substantiallyin a round shape. In the case of the narrow field of view display, whenthe light of this distribution 39 is made incident on the transparentand scattering switching element 22 in the transparent state, light of acircular distribution is transmitted through the transparent andscattering switching element 22 directly and light of the distribution39 is emitted. The light of this distribution 39 is transmitted throughthe liquid crystal panel 21 and emitted to realize the narrow field ofview display.

On the other hand, in the third modification of the first embodiment, asshown in FIG. 9, light emitted from the backlight 13 has an ellipticaldistribution 41 spreading widely in the Y direction compared with the Xdirection. When the light of this distribution 41 is made incident onthe louver 12, directivity of light spreading in the X direction isfurther improved by the louver 12 and, in particular, light distributedin the X direction changes to light of a distribution 42 having highdirectivity. In the case of the wide field of view display, when thelight of this distribution 42 is made incident on the transparent andscattering switching element 22 in the scattering state, the lightscatters to spread in the X direction to change to light of adistribution 43. The light of this distribution 43 is transmittedthrough the liquid crystal panel 21 and emitted to realize the widefield of view display. In addition, as shown in FIG. 10, when the lightof the distribution 41 emitted from the backlight 13 is made incident onthe louver 12, directivity of light spreading in the X direction isfurther improved by the louver 12 and, in particular, light distributedin the X direction changes to light of the distribution 42 having highdirectivity. In the case of the narrow field of view display, when thelight of this distribution 42 is made incident on the transparent andscattering element 22 in the transparent state, in particular, light ofa distribution having high directivity of light distributed in the Xdirection is transmitted through the transparent and scatteringswitching element 22 directly and light of the distribution 42 isemitted. The light of this distribution 42 is transmitted through theliquid crystal panel 21 and emitted to realize the narrow field of viewdisplay with respect to the X direction.

In the third modification of the first embodiment, compared with thefirst embodiment, since an amount of light, which is emitted from thebacklight 13 and absorbed by the louver 12, can be reduced, it ispossible to realize bright wide field of view display. In particular,since an amount of light of the backlight 13 is limited, the thirdmodification is effective in the case in which switching of an angle offield only in the X direction has to be realized. Components,operations, and effects in the third modification of the firstembodiment other than those described above are the same as those in thefirst embodiment.

Next, a second embodiment of the invention will be explained. FIG. 11 isa sectional view showing a liquid crystal display device in accordancewith the second embodiment. In the first embodiment described above, asshown in FIG. 1, the one louver 12, in which the transparent area 12 aand the absorption area 12 b of a stripe shape are arranged alternately,is provided between the backlight 13 and the transparent and scatteringswitching element 22. On the other hand, in the second embodiment, asshown in FIG. 11, a louver 15, in which a transparent area 15 a and anabsorption area 15 b of a stripe shape are arranged alternately in onedirection, and a louver 14, in which a transparent area 14 a and anabsorption area (not shown) of a stripe shape are arranged alternatelyin a direction orthogonal to an arrangement direction in the louver 15,are stacked to be provided between the backlight 13 and the transparentand scattering switching element 22. Consequently, in the secondembodiment, it is possible to improve directivity of light made incidenton the louver 12 not only in one direction but also in a directionorthogonal to the direction. Therefore, for example, it is possible torealize the narrow field of view display effectively not only in thehorizontal direction but also in the vertical direction. Components,operations, and effects in the second embodiment other than thosedescribed above are the same as those in the first embodiment.

Next, a third embodiment of the invention will be explained. FIG. 12 isa sectional view showing a liquid crystal display device in accordancewith the third embodiment. In the first embodiment described above, asshown in FIG. 1, the conventional PDLC layer 11, in which the liquidcrystal molecules 11 b are scattered uniformly in the polymer matrix 11a, is used as the planar transparent and scattering switching element22. On the other hand, in the third embodiment, as shown in FIG. 12, aPDLC layer 16, which is modulated such that distribution of liquidcrystal molecules 16 b scattered in a polymer matrix 16 a has unevennesscyclically, is used. In the modulated PDLC layer 16, for example, aportion where the liquid crystal molecules 11 b are dense and a portionwhere the liquid crystal molecules 11 b are sparse are repeatedcyclically in one direction. The modulated PDLC layer 16 scattersincident light intensely in the direction in which the portion where theliquid crystal molecules 11 b are dense and the portion where the liquidcrystal molecules 11 b are sparse are repeated cyclically. Consequently,it is possible to increase an angle of field in this direction.

It is possible to manufacture such a modulated PDLC layer 16 by usingthe same material as the conventional PDLC layer for a PDLC layer andsubjecting the PDLC layer to exposure and photo-curing via a photo-mask.Light is irradiated on the PDLC layer before curing via a photo-mask onwhich a linear pattern is formed cyclically. A part irradiated by thelight starts to harden. At this point, a concentration gradient of theliquid crystal molecules 16 b occurs between a hardening area and anot-hardening area. After the PDLC layer is subjected to the exposurefor a predetermined time via the photo-mask, the entire surface of thePDLC layer is exposed to light, whereby the modulated PDLC layer 16 isobtained. In this modulated PDLC layer 16, a mixture of two or morekinds of liquid crystal molecules with different sizes may be used asthe liquid crystal molecules 16 b. Components, operations, and effectsin the third embodiment other than those described above are the same asthose in the first embodiment.

Next, a fourth embodiment of the invention will be explained. FIG. 13 isa sectional view showing a liquid crystal display device in accordancewith the fourth embodiment. In the fourth embodiment, as shown in FIG.13, in addition to the structure of the liquid crystal display device inaccordance with the first embodiment, the liquid crystal display devicefurther includes a light source light intensity control unit 26 thatcontrols an amount of an electric current to be supplied to a white LED25 and adjusts an amount of light, that is, a luminance of the white LED25 and a transparent and scattering switching element control unit 27that switches ON and OFF of a voltage of the transparent and scatteringswitching element 22. The light source light intensity control unit 26and the transparent and scattering switching element control unit 27 areconstituted to be associated with each other. Components in the fourthembodiment other than those described above are the same as those in thefirst embodiment.

Next, operations of the liquid crystal display device in accordance withthe fourth embodiment constituted as described above will be explained.As shown in FIG. 13, in the case of the wide field of view display, thetransparent and scattering switching element control unit 27 does notapply a voltage to the transparent and scattering switching element 22.Consequently, light made incident on the transparent and scatteringswitching element 22 from the louver 12 is scattered. At this point, thelight source light intensity control unit 26 supplies an electriccurrent to the white LED 25 such that a front luminance, that is, aluminance at an angle of field of 0 degree of the liquid crystal panel21 takes a predetermined value. In the case of the narrow field of viewdisplay, the transparent and scattering switching element control unit27 applies a voltage to the transparent and scattering switching element22. Consequently, light made incident on the transparent and scatteringswitching element 22 from the louver 12 is transmitted through thetransparent and scattering switching element 22 directly. Therefore,when an amount of an electric current supplied to the white LED 25 isthe same, that is, an amount of light emitted from the backlight 13 isthe same, a front luminance of the liquid crystal panel 21 isexcessively large. Thus, the amount of electric current supplied to thewhite LED 25 is adjusted such that the front luminance of the liquidcrystal panel 21 in the case of the narrow field of view display takesas same value as that in the case of the wide field of view display.Consequently, in the fourth embodiment, the front luminance of theliquid crystal panel 21 is kept constant. Note that, in the case inwhich the white LED 25 is constituted by a blue LED and a yellowphosphor, an amount of light of the white LED 25 may be adjusted bypulse width modulation of an electric current. In the white LED 25constituted by the blue LED and the yellow phosphor, the yellow phosphoris excited by a part of blue light emitted by the blue LED to emityellow light, and the blue light and the yellow light are mixed togenerate white light. When an amount of an electric current is adjustedsuch that the front luminance of the liquid crystal panel 21 in the caseof the narrow field of view display takes a value equivalent to that inthe case of the wide field of view display, since an emission ratio ofthe blue light and the yellow light fluctuates, chromaticity change ofthe liquid crystal panel 21 occurs. On the other hand, when an amount oflight is adjusted by the pulse modulation, the adjustment of an amountof light is realized by adjusting a ratio of light emitting time, it ispossible to control chromaticity change of the liquid crystal panel 21.Operations and effects in the fourth embodiment other than thosedescribed above are the same as those in the first embodiment.

Next, a fifth embodiment of the invention will be explained. FIG. 14 isa sectional view showing a liquid crystal display device in accordancewith the fifth embodiment. In the fourth embodiment described above, asshown in FIG. 13, the white LED 25 and the linear light source 36 areused. On the other hand, in the fifth embodiment, as shown in FIG. 14, alight source, in which a red LED 28, a green LED 29, and a blue LED 30are arranged linearly and cyclically, is used instead of the linearlight source 36. The liquid crystal display device includes the lightsource light control unit 26 that controls amounts of electric currentsto be supplied to the red LED 28, the green LED 29, and the blue LED 30and adjusts amounts of lights, that is, luminances of the LEDs.Components in the fifth embodiment other than those described above arethe same as those in the fourth embodiment.

Next, operations of the liquid crystal display device in accordance withthe fifth embodiment constituted as described above will be explained.As shown in FIG. 14, lights emitted from the red LED 28, the green LED29, and the blue LED 30 are made incident on the backlight 13. Red,green, and blue are three primary colors of light, and lights of thesecolors are superimposed to form white light. The backlight 13 convertsincident light into planar light. In the case of the wide field of viewdisplay, this light is made incident on the transparent and scatteringswitching element 22 and scattered. At this point, since a degree ofscattering of light depends on a wavelength of the light, light with ashorter wavelength is scattered more intensely and light with a longerwavelength is less likely to be scattered. In other words, blue light islikely to be scattered and red light is less likely to be scattered.Therefore, a display image at the time when the liquid crystal panel isviewed from the front is reddish.

Thus, when light is scattered by the transparent and scatteringswitching element 22, for example, an amount of an electric currentsupplied to the blue LED 30 is increased to intensify blue light that islikely to be scattered, and an amount of an electric current supplied tothe red LED 28 is reduced to weaken red light that is less likely to bescattered. In this way, in the wide field of view display and the narrowfield of view display, intensity of lights emitted by the red LED 28,the green LED 29, and the blue LED 30 are adjusted in association withpresence or absence of application of a voltage to the transparent andscattering switching element 22, whereby a tint of a display image atthe time when the liquid crystal panel is viewed from the front can bekept constant. Operations and effects in the fifth embodiment other thanthose described above are the same as those in the fourth embodiment.

Next, a sixth embodiment of the invention will be explained. FIG. 15 isa sectional view showing a liquid crystal display device in accordancewith the sixth embodiment. In the sixth embodiment, in addition to thestructure of the liquid crystal display device in accordance with thefirst embodiment, transparent substrates 121 are provided on both sidesof the louver 12. In an example, a material of the transparentsubstrates 121 is polyethylene terephthalate. Components in the sixthembodiment other than those described above are the same as those in thefirst embodiment.

In the liquid crystal display device in accordance with the sixthembodiment constituted as described above, since the transparentsubstrates 121 are provided on both the sides of the louver 12, there isan effect that it is possible to improve resistance of the louver 12against changes in temperature and humidity, and reliability of theliquid crystal display device is improved. Operations and effects in thesixth embodiment other than those described above are the same as thosein the first embodiment. In addition, the sixth embodiment can also beapplied to the second to the fifth embodiments.

Next, a seventh embodiment of the invention will be explained. FIG. 16is a sectional view showing a liquid crystal display device inaccordance with the seventh embodiment. Whereas the louver and thetransparent and scattering switching element are fixed by a couple-facetape in the sixth embodiment, in the seventh embodiment, the louver 12having the transparent substrates 121 on both the sides thereof and thetransparent and scattering switching element 22 are bonded and, as aresult, formed integrally. Components in the seventh embodiment otherthan those described above are the same as those in the sixthembodiment.

In the liquid crystal display device in accordance with the seventhembodiment constituted as described above, the transparent substrates121 are provided on both the sides of the louver 12 and, in addition,the louver 12 and the transparent and scattering switching element 22are formed integrally. Thus, it is possible to improve resistance of thelouver 12 against changes in temperature and humidity and improvereliability of the liquid crystal display device. It is also possible toreduce thickness of the liquid crystal display device. Operations andeffects in the seventh embodiment other than those described above arethe same as those in the sixth embodiment.

Next, an eighth embodiment of the invention will be explained. FIG. 17is a sectional view showing a liquid crystal display device inaccordance with the eighth embodiment. Compared with the structure ofthe liquid crystal display device in accordance with the seventhembodiment, the eighth embodiment is characterized in that the louver 12and the transparent and scattering switching element 22 are integrallyformed and have a common substrate. In this example, the louver 12 hasthe transparent substrates 121 on both the sides thereof, and thesubstrate 121 of the louver 12 is also used as a transparent substrateon the transparent and scattering switching element 22 side. Thus, thetransparent and scattering switching element 22 does not have thetransparent substrate 9 on the louver 12 side. Components in the eighthembodiment other than those described above are the same as those in theseventh embodiment.

As described above, in the liquid crystal display device in accordancewith the eighth embodiment, it is possible not only to improvereliability as in the liquid crystal display device in accordance withthe seventh embodiment but also to reduce thickness of the liquidcrystal display device. In addition, since the number of substratesconstituting the liquid crystal display device can be reduced, it isalso possible to reduce weight of the liquid crystal display device.Operations and effects in the eighth embodiment other than thosedescribed above are the same as those in the seventh embodiment.

Next, a ninth embodiment of the invention will be explained. FIG. 18 isa sectional view showing a liquid crystal display device in accordancewith the ninth embodiment. Compared with the structure of the liquidcrystal display device in accordance with the eighth embodiment, in theninth embodiment, the louver 12 has only the transparent substrate 121common to the louver 12 and the transparent and scattering switchingelement 22 and does not have a transparent substrate on the backlight 13side. Components in the ninth embodiment other than those describedabove are the same as those in the eighth embodiment.

In the liquid crystal display device in accordance with the ninthembodiment constituted as described above, since the transparentsubstrate on the backlight 13 side of the louver 12 is not provided,reliability is lower than the reliability of the liquid crystal displaydevice in accordance with the eighth embodiment. However, since thetransparent substrate 121 is set on the transparent and scatteringswitching element 22 side, it is possible to improve reliabilitycompared with the first embodiment. In addition, compared with theliquid crystal display device in accordance with the eighth embodiment,in the ninth embodiment, since the transparent substrate of the louver12 can be removed, it is possible to further reduce thickness and weightof the liquid crystal display device. Operations and effects in theninth embodiment other than those described above are the same as thosein the eighth embodiment.

Next, a tenth embodiment of the invention will be explained. FIG. 19 isa sectional view showing a liquid crystal display device in accordancewith the tenth embodiment. Compared with the structure of the liquidcrystal display device in accordance with the first embodiment, theliquid crystal display device in accordance with the tenth embodiment isdifferent in that the high directivity backlight 213 described in themonthly magazine “Display” May 2004, pages 14 to 17 is used. Componentsin the tenth embodiment other than those described above are the same asthose in the first embodiment.

In the liquid crystal display device according to the tenth embodimentconstituted as described above, since the high directivity backlight 213with directivity improved two-dimensionally on a light emitting surfacethereof is used, it is possible to reduce a loss in absorption of lightby the louver 12 and realize bright display. In addition, since thedirectivity of the backlight is two-dimensional, it is also possible toshow an effect of switching of an angle of field concerning a directionorthogonal to the direction in which the transparent area and theabsorption area of the louver 12 are arranged alternately. Note that thehigh directivity backlight suitably used in the embodiment is notlimited to the high directivity backlight described in the monthlymagazine “Display” May 2004, pages 14 to 17, and it is possible to applyany backlight to the liquid crystal display device as long asdirectivity thereof is improved two-dimensionally.

FIG. 20 is a graph showing a result of an experiment in which a slightvoltage is applied to the transparent and scattering switching element22 in the scattering state to adjust a scattering property in the liquidcrystal display device in accordance with the tenth embodiment. In thegraph, a horizontal axis indicates an angle of field and a vertical axisindicates a luminance. A result indicated by a broken line is aluminance distribution in the case in which a voltage is not applied toa PDLC layer constituting a transparent and scattering switchingelement, and a result indicated by a solid line is a luminancedistribution in the case in which a slight voltage (in an example, 1volt) is applied to the PDLC layer. Note that the slight voltage in thiscontext means a small voltage compared with a voltage for bringing thetransparent and scattering switching element into a transparent state.Whereas a front luminance (a luminance in a 0° direction) in the case inwhich a voltage is not applied to the PDLC layer is 75 cd/m², a frontluminance in the case in which a slight voltage is applied is improvedto 120 cd/m². On the other hand, in an oblique direction, morespecifically, in a range from +25° to +80° or a range from −25° to −80°,although a luminance in the case in which a voltage is applied slightlyfalls, a degree of the fall in the voltage is extremely small, and aluminance of substantially the same degree as that in the case in whicha voltage is not applied is secured. This indicates that it is possibleto improve a luminance in a front direction significantly withoutdecreasing the luminance in the oblique direction significantly byapplying a slight voltage at the time of scattering of the transparentand scattering switching element to slightly decrease the scatteringproperty. This result is effective in the case in which a frontluminance falls in the wide field of view display, due to limited amountof light of the back light. Although the tenth embodiment is explained,the explanation is not limited to the tenth embodiment but is applicableto the other embodiments as well. Operations and effects in the tenthembodiment other than those described above are the same as those in thefirst embodiment.

Next, an eleventh embodiment of the invention will be explained. FIG. 21is a perspective view showing a portable terminal device mounted withthe liquid crystal display device of the invention. As shown in FIG. 21,a liquid crystal display device 100 of the invention is mounted on, forexample, a cellular phone 90.

The liquid crystal display device of the invention can be applied to aportable device such as a cellular phone and makes it possible toperform display for switching an angle of field. In particular, in thecase in which the liquid crystal display device of the invention ismounted on a cellular phone, a transparent area and an absorption areaof a louver serving as a ray direction regulating element are arrangedalternately at least in a lateral direction of the cellular phone,whereby it is possible to switch the wide field of view display and thenarrow field of view display with respect to the lateral direction ofthe cellular phone. This makes it possible to prevent a peep by otherpeople from the lateral direction in public transportation facilitiesand the like. Note that the portable device is not limited to thecellular phone, and it is possible to apply the liquid crystal displaydevice to various portable terminal devices such as a Personal DigitalAssistant (PDA), a game machine, a digital camera, and a digital videocamera. Moreover, the portable device mounted with the liquid crystaldisplay device of the invention may have a setting for changing amountsof a light source at the time of the wide field of view display and thenarrow field of view display independently from each other and may becapable of setting light emitting ratios of the light source in both thecases. Consequently, a user can set an optimum angle of field accordingto an environment of use. Furthermore, the portable device may havemeans for detecting residual battery power and have control means thatcan automatically change an angle of field according to the detectedresidual battery power. As described above, in the liquid crystaldisplay device of the invention, since an electric power can be reducedmore at the time of narrow field of view display than at the time of thewide field of view display, it is possible to reduce power consumptionby automatically changing the wide field of view display to the narrowfield of view display when residual battery power is low and extend anoperating time of the portable device.

Next, a twelfth embodiment of the invention will be explained. FIG. 22is a plan view showing the transparent and scattering switching element22 of a liquid crystal display device in accordance with the twelfthembodiment. Compared with the structure of the first embodiment, thetwelfth embodiment is different in that at least one side of theelectrodes 10 of the transparent and scattering switching element 22 ismachined in a line shape. Components in the twelfth embodiment otherthan those described above are the same as those in the firstembodiment.

In the liquid crystal display device in accordance with the twelfthembodiment constituted as described above, it is possible to performswitching of transparent and scattering partially in plane by applyingdifferent voltages to the electrodes 10 machined in a line shape of thetransparent and scattering switching element 22. Consequently, forexample, it is possible to change the transparent and scatteringswitching element 22 to transparent only for a portion whereconfidential information is displayed on the basis of image informationdisplayed on the liquid crystal display device to perform the narrowfield of view display. Note that a shape of the electrodes 10 of thetransparent and scattering switching element 22 is not limited to theline shape but may be a block shape.

Consequently, it is possible to switch the narrow field of view displayand the wide field of view display in a block shape. In addition, in thetwo transparent substrate arranged above and below the PDLC layer, theelectrodes may be machined in a line shape, respectively, and arrangedsuch that longitudinal directions thereof are orthogonal to each other.This makes it possible to perform passive matrix drive for thetransparent and scattering switching element 22 and switch an angle offield of an arbitrary portion on a screen. Operations and effects in thetwelfth embodiment other than those described above are the same asthose in the first embodiment.

Note that, as the PDLC layer that is used in the respective embodimentsand the respective modifications, a PDLC layer, which is in thescattering state when a voltage is not applied thereto and is in thetransparent state at the time of voltage application. Consequently, thetransparent and scattering switching element does not consume electricpower when the transparent and scattering switching element is in astate in which the transparent and scattering switching element scattersincident light. Thus, since the electric power is allocated to thebacklight power supply, it is possible to improve brightness of theplanar light source at the time of the scattering state. However, a formof the PDLC layer is not limited to the above, and a PDLC layer, whichis in the transparent state when a voltage is not applied thereto and inthe scattering state at the time of voltage application, may be used.Such a PDLC layer is obtained by exposing a material to light to hardenthe material while applying a voltage thereto. Consequently, in theportable information terminal, it is unnecessary to apply a voltage tothe PDLC layer and it is possible to control power consumption in thenarrow field of view display that is used frequently.

In addition, cholesteric liquid crystal, ferroelectric liquid crystal,or the like may be used as the liquid crystal molecules used in the PDLClayer. The liquid crystal keeps an orientation state at the time when avoltage is applied thereto even if an applied voltage is turned OFF andhas a memory property. It is possible to reduce power consumption byusing such a PDLC layer.

As shown in FIG. 23, a direction in which the transparent area and theabsorption area of the ray direction regulating element and a pixelarrangement direction of the liquid crystal display panel may be notparallel to each other. Consequently, it is possible to reduce moiré dueto the ray direction regulating element and the display panel andimprove an image quality of the liquid crystal display device.

The display panel, which is used in combination with the planar lightsource of the invention, is not limited to the transparent liquidcrystal panel. Any display panel may be used as long as the displaypanel uses a backlight. In particular, it is possible to use a liquidcrystal panel with less dependency on an angle of field suitably. As anexample of a mode of such a liquid crystal panel, in a lateral electricfield mode, there are an IPS (In-Plane Switching) system, an FFS (FringeField Switching) system, an AFFS (Advanced Fringe Field Switching)system, and the like. In addition, in a vertical orientation mode, thereare an MVA (Multi-domain Vertical Alignment) system, a PVA (PatternedVertical Alignment) system, an ASV (Advanced Super V) system, and thelike in which a liquid crystal panel is multi-domained to reducedependency on an angle of field. It is also possible to use theinvention in a liquid crystal display panel of a film compensation TNmode suitably. By using these liquid crystal panels with less dependencyon an angle of field, it is possible to control tone reversal of displaywhen the transparent and scattering switching element is in thescattering state and improve visibility. In addition, the liquid crystalpanel is not limited to the transmission liquid crystal panel, and anypanel may be used as long as the panel has a transmission area in eachpixel. It is also possible to use a semi-transmission liquid crystalpanel, a micro-transmission liquid crystal panel, and a micro-reflectionliquid crystal panel that have a reflection area in a part of eachpixel. Note that the reflection area does not always need to havereduced dependency on an angle of field, and only the transmission areamay have reduced dependency on an angle of field.

1. A planar light source comprising: a backlight that emits light in aplanar shape; a ray direction regulating element that regulates adirection of light made incident from the backlight and emits the light,whereby a directivity of the light is improved, said ray directionregulating element comprising a transparent area for transmitting lightand an absorption area for absorbing light are formed alternately in adirection parallel to a surface of the ray direction regulating element;and a transparent and scattering switching element that is switchablebetween a state in which light which is transmitted by the ray directionregulating element and made incident on said switching element istransmitted and a state in which the light is scattered; wherein lightemitted by the backlight spreads radially in an elliptical shape withrespect to a direction perpendicular to an emission surface of saidbacklight, and wherein the transparent area and the absorption area ofthe ray direction regulating element are formed alternately in adirection parallel to a short diameter direction of the ellipticalshape.
 2. The planar light source according to claim 1, wherein, in theray direction regulating element, the transparent area is provided inthe absorption area in a matrix shape in a direction perpendicular to asurface of the ray direction regulating element.
 3. The planar lightsource according to claim 2, wherein a shape of the transparent areacomprises one of a circular shape, elliptical shape, square shape, andrectangular shape in a direction perpendicular to a surface of the raydirection regulating element.
 4. The planar light source according toclaim 1, wherein the ray direction regulating element has a first layerin which the transparent area and the absorption area are formedalternately and a second layer in which the transparent area and theabsorption area are formed alternately in a direction perpendicular tothe first layer.
 5. The planar light source according to claim 1,wherein the transparent and scattering switching element and the raydirection regulating element are formed integrally.
 6. The planar lightsource according to claim 5, wherein the transparent and scatteringswitching element and the ray direction regulating element have a commonsubstrate.
 7. The planar light source according to claim 6, wherein asubstrate of the ray direction regulating element is only a substratecommon to the ray direction regulating element and the transparent andscattering switching element.
 8. The planar light source according toclaim 1, wherein the transparent and scattering switching elementcomprises a polymer dispersed liquid crystal layer formed between a pairof electrodes and is in the state in which the transparent andscattering switching element scatters incident light when a voltage isnot applied between the flat electrodes, and wherein a voltage isapplied to the transparent and scattering switching element when thetransparent and scattering switching element is used in the transparentstate.
 9. The planar light source according to claim 1, furthercomprising: a linear light source formed on a first side of saidbacklight for emitting light which is incident on said first side ofsaid backlight, wherein said transparent area comprises plural firststripe portions and said absorption area comprises plural second stripeportions which are alternately formed and extend between said first sideof said backlight and a second side of said backlight which is oppositesaid first side.
 10. The planar light source according to claim 1,wherein said transparent and scattering switching element comprisesscattering liquid crystal molecules formed in a polymer matrix.
 11. Adisplay device comprising: a backlight that emits light in a planarshape; a ray direction regulating element that regulates a direction oflight made incident from the backlight and emits the light, whereby adirectivity of the light is improved, said ray direction regulatingelement comprising a transparent area for transmitting light and anabsorption area for absorbing light which are formed alternately in adirection parallel to a surface of the ray direction regulating element;a transparent and scattering switching element that is switchablebetween a state in which light which is transmitted by the ray directionregulating element and made incident on said switching element istransmitted and a state in which the light is scattered; and a liquidcrystal panel that displays an image with light made incident from thetransparent and scattering switching element, and wherein light emittedby the backlight spreads radially in an elliptical shape with respect toa direction perpendicular to an emission surface of said backlight, andwherein in the ray direction regulating element, the transparent areaand the absorption area are formed alternately in a direction parallelto a short long diameter direction of the elliptical shape.
 12. Thedisplay device according to claim 11, wherein, in the ray directionregulating element, the transparent area is provided in the absorptionarea in a matrix shape in a direction perpendicular to a surface of theray direction regulating element.
 13. The display device according toclaim 12, wherein a shape of the transparent area comprises one of acircular shape, elliptical shape, square shape, and rectangular shape ina direction perpendicular to a surface of the ray direction regulatingelement.
 14. The display device according to claim 11, wherein the raydirection regulating element has a first layer in which the transparentarea and the absorption area are formed alternately and a second layerin which the transparent area and the absorption area are formedalternately in a direction perpendicular to the first layer.
 15. Aportable terminal device, comprising: the planar light source accordingto claim 1, wherein the transparent area and the absorption area of theray direction regulating element are formed alternately in a lateraldirection of the portable terminal device.
 16. A ray direction switchingelement for a planar light source including a backlight, comprising: aray direction regulating element for regulating a direction of incidentlight and emitting light, whereby a directivity of the light isimproved, said ray direction regulating element comprising a transparentarea for transmitting light and an absorption area for absorbing lightwhich are fanned alternately in a direction parallel to a surface of theray direction regulating element; and a transparent and scatteringswitching element for switching a state in which light made incidentfrom the ray direction regulating element is transmitted and a state inwhich the light is scattered, wherein said ray direction regulatingelement and said transparent and scattering switching element areintegrally formed, wherein the incident light spreads radially in anelliptical shape with respect to an incident surface of said backlight,and wherein the transparent area for transmitting light and theabsorption area for absorbing light are formed alternately in adirection parallel to a short diameter direction of the ellipticalshape.
 17. The ray direction switching element according to claim 16,wherein the transparent and scattering switching element and the raydirection regulating element are formed on a common substrate.
 18. Theray direction switching element according to claim 17, wherein asubstrate of the ray direction regulating element comprises a substratecommon only to the ray direction regulating element and the transparentand scattering switching element.